Anyone have any thoughts on covering sumps to avoid evaporation? I was losing a bit of water from my old sump, but have just installed a new one with an open water surface area of 600x400mm. I have my display tank covered, but the sump is currently lidless, so I am losing alot of water in to the air. I am thinking of covering it, but i dont want to limit the amount of surface O2 transfer by limiting airflow over the surface of the water. I also worry about where all of that water is going... my computers are in the same room as my tanks.